libalsa: set cpp_info.resdirs & minor improvements

[SpaceIm]

see conan-io/docs#2767

---

• I've read the guidelines for contributing.
• I've followed the PEP8 style guides for Python code in the recipes.
• I've used the latest Conan client version.
• I've tried at least one configuration locally with the conan-center hook activated.

[github-actions]

Hooks produced the following warnings for commit ac05807

libalsa/1.1.9

post_package(): WARN: [SHORT_PATHS USAGE (KB-H066)] The file './res/alsa/ucm/ASUSTeKCOMPUTERINC.-T100HAN-1.0-T100HAN/ASUSTeKCOMPUTERINC.-T100HAN-1.0-T100HAN.conf' has a very long path and may exceed Windows max path length. Add 'short_paths = True' in your recipe.
post_package(): WARN: [SHORT_PATHS USAGE (KB-H066)] The file './res/alsa/ucm/cube-i1_TF-Defaultstring-CherryTrailCR/cube-i1_TF-Defaultstring-CherryTrailCR.conf' has a very long path and may exceed Windows max path length. Add 'short_paths = True' in your recipe.
post_package(): WARN: [SHORT_PATHS USAGE (KB-H066)] The file './res/alsa/ucm/TECLAST-X80Pro-Defaultstring-CherryTrailCR/TECLAST-X80Pro-Defaultstring-CherryTrailCR.conf' has a very long path and may exceed Windows max path length. Add 'short_paths = True' in your recipe.
post_package(): WARN: [SHORT_PATHS USAGE (KB-H066)] The file './res/alsa/ucm/bytcr-rt5651-mono-spk-in2-mic-hp-swapped/bytcr-rt5651-mono-spk-in2-mic-hp-swapped.conf' has a very long path and may exceed Windows max path length. Add 'short_paths = True' in your recipe.
post_package(): WARN: [SHORT_PATHS USAGE (KB-H066)] The file './res/alsa/ucm/LENOVO-80XF-LenovoMIIX320_10ICR-LNVNB161216/LENOVO-80XF-LenovoMIIX320_10ICR-LNVNB161216.conf' has a very long path and may exceed Windows max path length. Add 'short_paths = True' in your recipe.

[conan-center-bot]

All green in build 3 (ac058075aedbfa7c511184db4773f041d2f26fb4):

• libalsa/1.2.7.2@:
  All packages built successfully! (All logs)

• libalsa/1.2.5.1@:
  All packages built successfully! (All logs)

• libalsa/1.2.7@:
  All packages built successfully! (All logs)

• libalsa/1.2.4@:
  All packages built successfully! (All logs)

• libalsa/1.2.2@:
  All packages built successfully! (All logs)

• libalsa/1.1.9@:
  All packages built successfully! (All logs)